1. Field of the Invention
The present invention relates to a stacker crane.
2. Description of the Related Art
A conventional automated warehouse includes, for example, a pair of racks, a stacker crane, a warehousing station, and a delivery station. The pair of racks is spaced apart by a prescribed spacing in the forward-rearward direction. The stacker crane is provided moveably in the left-right direction between the front and rear racks. The warehousing station is disposed on a side of one of the racks. The delivery station is disposed on a side of the other one of the racks. The racks have numerous article storage shelves at the top, bottom, left, and right.
The stacker crane includes a travelling truck, a lift platform that is freely elevatable along a mast provided to the travelling truck, and an article transfer apparatus (e.g., a slide fork that is slidably provided in the forward-rearward direction) that is provided to the lift platform. The travelling truck principally includes a lower frame that is guided by and travels along a travelling rail (e.g., refer to Japanese Unexamined Patent Application Publication No. 2003-237909). The lower frame has a pair of parallel side frames, the side frames being linked to one another at a center portion in the longitudinal direction.
The mast and the lower frame of a conventional stacker crane are bolted to one another by a flange. In addition, reinforcing ribs are welded to the mast. A lifting drive mechanism (including a lifting drive motor) is welded to the mast, and a wheel is joined, as a wheel unit, to the lower frame.
In recent years, there has been a demand to achieve high performance in stacker cranes (high speed performance and high acceleration-deceleration performance of the crane). Furthermore, achieving such performance also increases the stress that acts upon a mast base portion, and therefore there is also a demand for reinforcing ribs that are strong. However, simply increasing the strength of the reinforcing ribs constrains the attachment of the lifting drive portion and the wheels due to the enlarged reinforcing ribs.